Thermoplastic resins including polyolefin, ABS and vinyl chloride resins are universally used as packaging materials in various forms such as film, bag, etc. and as raw materials for automotive and other industrial parts. However, these resins have the serious drawback that they generally have high electric resistance values and, therefore, are easily charged electrostatically on friction for dust particles to stick.
Therefore, attempts have recently been made to impart antistatic properties to thermoplastic resin products by using antistatic agents in the following alternative ways (1) and (2).
(1) Coating the surface of a resin product with an antistatic agent and drying it. PA1 (2) Milling an internal antistatic agent into a matrix resin. PA1 (A) 100 parts by weight of a thermoplastic resin, PA1 (B) 3-30 parts by weight of a cationic copolymer comprising a structural unit of formula (1) and a structural unit of formula (3) ##STR3## (wherein Z represents ##STR4## R.sup.2 represents ethylene or propylene; R.sup.3 and R.sup.4 independently represent methyl; R.sup.5 represents linear lower alkyl or aralkyl; X represents halogen, CH.sub.3 OSO.sub.3, CH.sub.3 CH.sub.2 OSO.sub.3, or R.sup.6 SO.sub.3, where R.sup.6 represents C.sub.1-8 alkyl or aralkyl), said ethylene unit of formula (1) and cationic unit of formula (3) accounting for 80-98 mol % and 2-20 mol %, respectively, of the copolymer, and having a weight-average molecular weight of 1,000-50,000, and PA1 (C) 0.1-10 parts by weight of a copolymer comprising at least one unit each per molecule of a structural unit of formula (4) ##STR5## (wherein R.sup.7 represents hydrogen or methyl; R.sup.8 represents hydrogen, C.sub.1-42 alkyl, phenyl, or COOR.sup.9, where R.sup.9 represents C.sub.1-4 alkyl) and a structural unit of formula (5) ##STR6## (wherein Y represents O or N-R.sup.10, where R.sup.10 represents hydrogen, C.sub.1-14 alkyl, aryl, aralkyl, R.sup.2 -N.sup..sym. R.sup.3 R.sup.4 R.sup.5.X.sup..crclbar., or R.sup.2 -NR.sup.3 R.sup.4 ; R.sup.2 .about.R.sup.5 and X are as defined hereinbefore) and having a weight-average molecular weight of 800-200,000. PA1 (A) 100 parts by weight of a thermoplastic resin, PA1 (B) 3-30 parts by weight of a cationic copolymer comprising a structural unit of formula (1), a structural unit of formula (2), and a structural unit of formula (3) ##STR7## (wherein R.sup.1 represents methyl or ethyl and may be the same or different over all structural units) ##STR8## wherein Z represents ##STR9## R.sup.2 represents ethylene or propylene; R.sup.3 and R.sup.4 independently represent methyl; R.sup.5 represents linear lower alkyl or aralkyl; X represents halogen, CH.sub.3 OSO.sub.3, CH.sub.3 CH.sub.2 OSO.sub.3, or R.sup.6 SO.sub.3, where R.sup.6 represents C.sub.1-8 alkyl or aralkyl), said ethylene unit of formula (1), acrylate unit of formula (2), and cationic unit of formula (3) accounting for 79.9-97.9 mol %, not more than 15 mol %, and 2-20 mol %, respectively, of the copolymer, and having a weight-average molecular weight of 1,000-50,000, and PA1 (C) 0.1-10 parts by weight of a copolymer comprising at least one unit each per molecule of a structural unit of formula (4) and a structural unit of formula (5) ##STR10## (wherein R.sup.7 represents hydrogen or methyl; R.sup.8 represents hydrogen, C.sub.1-42 alkyl, phenyl, or COOR.sup.9, where R.sup.9 represents C.sub.1-4 alkyl) ##STR11## (wherein Y represents O or N-R.sup.10, where R.sup.10 represents hydrogen, C.sub.1-14 alkyl, aryl, aralkyl, R.sup.2 -N.sup..sym. R.sup.3 R.sup.4 R.sup.5.X.sup..crclbar., or R.sup.2 -NR.sup.3 R.sup.4 ; R.sup.2 .about.R.sup.5 and X are as defined hereinbefore) and having a weight-average molecular weight of 800-200,000. PA1 (A) 100 parts by weight of a styrenic thermoplastic resin, PA1 (B) 1-15 parts by weight of an antistatic cationic copolymer comprising a structural unit of formula (1) and a structural unit of formula (3), ##STR12## (wherein Z represents ##STR13## R.sup.2 represents ethylene or propylene; R.sup.3 and R.sup.4 independently represent methyl; R.sup.5 represents linear lower alkyl or aralkyl; X represents halogen, CH.sub.3 OSO.sub.3, CH.sub.3 CH.sub.2 OSO.sub.3, or R.sup.6 SO.sub.3, where R.sup.6 represents C.sub.1-8 alkyl or aralkyl), said ethylene unit of formula (1) and cationic unit of formula (2) accounting for 80-98 mol % and 2-20 mol %, respectively, of the copolymer, and having a weight-average molecular weight of 1,000-50,000, and PA1 (C) 0.05-5 parts by weight of a copolymer comprising at least one unit each per molecule of a structural unit of formula (4) and a succinic anhydride unit of formula (5) either in the backbone chain or in a side chain ##STR14## (wherein R.sup.7 represents hydrogen or methyl; R.sup.8 represents hydrogen or C.sub.1-42 alkyl and may mean a mixture thereof within the same copolymer molecule). ##STR15## and having a weight-average molecular weight of 800-200,000. PA1 (A) 100 parts by weight of a styrenic thermoplastic resin, PA1 (B) 1-15 parts by weight of an antistatic cationic copolymer comprising a structural unit of formula (1), a structural unit of formula (2), and a structural unit of formula (3), ##STR16## (wherein R.sup.1 represents methyl or ethyl and maybe the same or different over all structural units) ##STR17## (wherein Z represents ##STR18## R.sup.2 represents ethylene or propylene; R.sup.3 and R.sup.4 independently represent methyl; R.sup.5 represents linear lower alkyl or aralkyl; X represents halogen, CH.sub.3 OSO.sub.3, CH.sub.3 CH.sub.2 OSO.sub.3, or R.sup.6 SO.sub.3, where R.sup.6 represents C.sub.1-8 alkyl or aralkyl ), said ethylene unit of formula (1), acrylate unit of formula (2), and cationic unit of formula (3) accounting for 79.9-97.9 mol %, not more than 15 mol %, and 2-20 mol %, respectively, of the copolymer, and having a weight average molecular weight of 1,000-50,000, and PA1 (C) 0.05-5 parts by weight of a copolymer comprising at least one unit each per molecule of a structural unit of formula (4) and a structural unit of formula (5) either in its backbone chain or in a side chain ##STR19## (wherein R.sup.7 represents hydrogen or methyl; R.sup.8 represents hydrogen or C.sub.1-42 alkyl and my mean a mixture thereof within the same copolymer molecule). ##STR20## and having a weight-average molecular weight of 800-200,000.
In method (1), a surfactant solution is used as the antistatic agent. However, such an antistatic agent is readily removed upon washing of the resin product so that no permanent antistatic property can be imparted.
In method (2), glycerin fatty acid esters, sorbitan fatty acid esters, alkyldiethanolamides, sodium alkylbenzenesulfonates, alkylimidazole quaternary salts, etc. are generally used as the internal antistatic agent. In such cases, even if the antistatic agent on the resin surface is washed off, the loss is made up for by a fresh supply of the antistatic agent bleeding out from within the resin so that the imparted antistatic properties are retained for a comparatively long time.
However, when such an internal antistatic agent is employed, it takes time after washing for the antistatic properties to be restored and in the event of excessive bleeding-out of the antistatic agent, the resin becomes tacky to attract dust rather more readily. Moreover, because these antistatic agents are generally of low molecular weight, the antistatic agent added is evaporated by heat in the course of high-temperature molding so that the antistatic agent must be incorporated in a greater amount than necessary and it has been found difficult to optimize the level of addition of the antistatic agent.
Recently, to overcome the above-mentioned disadvantages of the conventional antistatic technology involving the use of an internal antistatic agent, a large number of resin compositions with perpetuated antistatic properties have been developed by alloying a thermoplastic resin with a macromolecular compound containing antistatic functional groups which is generally called a permanent antistatic agent. Among the antistatic agents heretofore proposed are a polymethyl methacrylate in which 20-80 mol % of methoxy groups have been modified by diethanolamine (JP-A-01170603), an alkoxy-polyethylene glycol methacrylate graft copolymer (JP-B-58039860), a cationic polymer derived from a styrene-maleic anhydride copolymer by imidation and subsequent quaternization (JP-B-01029820), a comb-shaped copolymer prepared by alloying a macromolecular monomer available on conversion of the terminal carboxyl groups of a carboxy-terminated polymethyl methacrylate to methacryloyl groups using glycidyl methacrylate with an aminoalkyl-acrylic acid ester or acrylamide or a quaternized cationic version thereof (JP-A-62121717), and a polyalkylene oxide chain-containing polyetheresteramide (JP-B-04005691), and a variety of compositions containing any of these antistatic agents in combination with various thermoplastic resins have been proposed.
However, the permanent antistatic agents mentioned above invariably detract from the strength, elongation and other physical properties of resins and, moreover, are not fully satisfactory in antistatic performance and its endurance.
In addition, an attempt has been made to provide an electrically conductive resin product by molding a copolymer composed of 40-90 weight % of ethylene and 60-10 weight % of a dialkylaminoalkyl (meth)acrylamide and immersing the molding in an inorganic acid salt solution (JP-A-64054041).
However, this technology involves an additional step of immersion and has proved disadvantageous in commercial application.
To obviate the above drawbacks of the conventional macromolecular compound containing antistatic functional groups, the inventors of the present invention proposed a polyethylene copolymer having a quaternary ammonium base-containing acrylamide unit (JP-A-04198308). With this copolymer, excellent antistatic properties and satisfactory endurance of the properties are assured and, in the form of film, high strength and elongation characteristics are achieved, thus overcoming most of the above-mentioned disadvantages. However, when the resin composition is injection- or otherwise molded, the thermal deformation and other thermal characteristics are not as satisfactory as desired, thus interfering with the application of the composition to three-dimensional articles.
Meanwhile, the inventors of the present invention further proposed a thermoplastic resin composition insuring improvements in the thermal characteristics of moldings (JP-A-06212079) but When this composition is applied to the production of large-sized articles such as TV cabinets and copying machine housings or films of large surface area, the distribution of antistatic properties (e.g. surface resistivity) is sometimes not uniform.
Meanwhile, in view of the adverse effects of an antistatic agent added on the matrix resin (deterioration of physical properties of the resin) and production economics, reductions in the level of addition of antistatic chemicals have been demanded and much research for meeting the demand is being carried out.
Developed in view of the above state of the art, the present invention has for its object to provide a thermoplastic resin composition which is improved in thermal characteristics (for example, reduced liability to undergo thermal deformation) and highly antistatic with a minimum of variation in the distribution of antistatic properties even if molded into an article of large surface area (uniformity of antistaticity) at a reduced addition level of an antistatic agent.